Combined phase converter and frequency changer



July 1 1924. 1,499,918

C. LE G. FORTESCUE COMBINED PHASE CONVERTER AND FfiEQUENCY CHANGER Filed Feb. 5, 1921 INVENTOR WITNESSES:

- CZar/esLe'Z'Zrtcscue ATTORNEY Patented July '1 1924.

UNITED sT Frj 1,499,918 PATENT OFFICE.

CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO WEST- INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVANIA.

COMBINED PHASE CONVERTER AND FREQUENCY CHANGER.

Application filed February a, 1921. Serial No. 442,761.

' To all whom it may concern:

Be it known that I, CHARLES LE G. Fonrnsonn, a subject of the King of Great Britain, and a resident of Pittsburgh, in the 8 county of Allegheny and State of Pennsyl- Vania, have invented a new and useful Improvement in Combined Phase Converters and Frequency Changers, of which the following is a specification.

My invention relates to a combined phase converter and frequency changer which is particularly adapted for accelerating induction motors.

One of the objects of my invention is to 15 provide a system for converting from singlephase currents or unbalanced polyphase currents to balanced polyphase currents, with provision for varying the frequency of said balanced polyphase' currents.

Another object of my invention is to provide a frequency, changer in which the employment of resistanceelements is avoided. Still another object of my invention is to rovide a combined phase converter and I requenoy changer which is capable of operating, at all times, at unity power-factor or at any other desired power-factor.

Other objects, as well as the details of my invention, will be apparent from the follow- 50 ing description, when read in connection with the accompanying drawings.

The single figure of the drawings is a diagrammatic view of apparatus and connections embodying one form of my invention.

Single-phase power, or unbalanced polyphase. power may be supplied by an means whatsoever. I have shown a sing e-phase transformer 5, the primary winding 6 of which derives energy from a trolley wire 7 and ground 8. The secondary winding 9 of' the transformer supplies power to my converter 5 stem.

The com ined phase converter and freuenoy changer is a dynamo-electric mal5 0 e 10, similar to a rotary converter, said machine having a polyphase commutated perimary member 11 and a secondary memr 12. The primary winding may be con nected, at diametrically opposite points, to

o slip rings 13 and 14, and, at three symmetrical ints, toslip rings 14, 15 and 16.

e commutator with brushes 18, 19 and 20 which are carried by a rotating system, such as a gear wheel cylinder 17 cooperates which are small re 21. The speed of the revolving brushes is controlled by means of a motor 22, which is shown as a polyphase motor energized from I .to utilize only the forwardly rotating sys tern, it is necessary to provide the machine with a secondary member having good damper windings for damping out the double-frequency currents induced therein by the backwardly rotating system.

In the illustrated embodiment of my invention, I have indicated the secondary member 12 as having a single distributed, star-connected winding 23, 24, 25. Phase windings 24 and 25 are short-circuited and connected to phase winding 23 in series with a variable battery 26. If desired, the battery may be shunted by a condenser 27 or by a condenser 27 and an inductance 28 which may be tuned, if desired, to' the double-frequency currents, in order to provide a lowimpedance path therefor. This is particularly necessary in case a rheostat is used in connection with the variable battery 26. It

is to be understood, of course, that the illustrated arran ement is only suggestive and thereof. 7 c

When the brush system is stationary, the machine 10 operates as a rotary converter, and direct-current electromotive forces appear at the brushes 18, 19 and 20. When the brushes are revolved in the direction of the rotor member 11 of the main machine, polyphase alternating currents appear at the commutator brushes, said polyphase currents havin a frequency proportional to the speed 0 the brushes. At synchronous speed, the brushes deliver pol phase currents of line frequency, an at oversynchronous speed, the brushes deliver currents of a correspondingly higher frequency.

However, when lyphase. power is su plied from a machine of the character escribed, negative-ghase-sequenoe currents,

/ magnetic cou ling between the rotor and the stator. onsequently, in s ite of the good damper windings, 'sma negativephase-sequence electromotive forces appear at the rotating brushes having a frequency proportional to the line frequency plus the relative s eed of the brushes.

If, desired, the negative-phase-sequence currents tending to flow in the leads con nected to the brushes may be eliminated by means of a series balancer 30-, such as is described in my copending application,

Serial No. 258,578, filed October 17, 1918. The series balancer is an induction machine .comprisin a series-connected polyphase primary win ing 31 and a seconda member 32 which has a lgigvod damper winding 33 and rotates bac ardl speed corresponding to e frequency of the negative-phase-sequence currents. The capacity of the series balancer 30 may be very small, as compared with that of the mam machine 10, since the negative-phase-sequence electromotive forces are sma The series balancer 30 tends to run by itself at the proper speed, rovided it is once started in the backwar direction. The series balancer may, therefore, be left to run by itself or it may be driven by a motor having approximately the correct speed ad-v ju'stment to supply a. substantially constant torque sufiicient to overcome the frictional and other losses of the series balancer at all s eeds at which it must run. By me-= chamcal systems of gearin which are well hown in the art, I may d rive the rotor of the series balancer at the proper speeds directly from the rotatin brush system.

A more elaborate -e ectrical scheme for driving the rotor of the series balancer is shown in the drawing. It is understood that the frequency of the negative base-sequence currents, which determine tne speed of the series balancer, varies from twicethe line frequency, when the brushes are at stand-still, to line frequency -when the brushes are revolvin at synchronous speed.

In the drawing, t e rotor. member '32 of the series balancer is shown as being'mounted on the shaft of a series, direct-current motor 34, deriving energy from a battery 35. The speed of the motor 34 is controlled by a varlable resistor 36, the effectiveportion of which is controlled b means of a s eed governor 38, which is driven from the aft of. the motor 22. In this manner, the resistdnce of the element 36 is increased with an increase in the speed of the rotating brush system, thus decreasing the speed of the motor 34,-as is desired. I

.When the above-described converte system is employed to control the speed i an at synchronous 'bodiment of in induction motor or motors, as in locomotive service, it may be desirable to utilize the rotating brush system for acceleratin poses only, permanent runnin con itions being-obtained b means of a ouble-throw switch 40, where y the load may be transferred from the rotating brush 5 stem to the slip rings 14, 15, 16 when t e brush system is rotating at synchronous speed. Under the last-mentioned conditions, the brushes may be lifted entirely away from the commutator cylinder 17, if desired. I have indicated the load as com rising a polyphase induction motor 41, riving a locomotive wheel 42.

The claims in this a plication are drawn to cover the phase an frequency converting machine 10, or the combination of this machine with two systems or translating devices having diiferent phase numbers or frequencies. The system for controlling the speed of the induction motor 41, and combinations including theserie's balancer 30,

are claimed in my co-gendin'g application,-

commutator brus es at synchronous speed for zero frequency.

It is also to be understood that the directcurrent excitin means for the converter 10 is not essentia, since good balancing may owever, the di-' power-factor compensation, as well as for im roving the balancing action.

he frequency-changing system herein described is particularly applicable for induction-motor control, such as is necessary I in railway work, since the standstill torque of an induction motor, with any given rimary current, is inversely proportiona to the fre uency. It is thus seen that I have provide in a single constant-speed machine, a particularly advantageous means for acceleratingl the driving motors of locomotives, toget er with means for transferring the load to an ordinary phase-converter con nection without frequency conversion.

While I have referred to a preferred eminvention in order to illustrate the principles thereof, it is to be understood that numerous changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, as defined in the a pended claims. I, therefore, desire that o y such restrictions shall be placed upon my invention as are set, forth in the claims, or are imposed by the prior art.

I claim as my invention:

1. The combination with two alternatingeurrent systems, only one of which has substantially balanced polyphase power, of a constant-speed dynamo-electric machine having a polyaxially closed-circuit secondary winding and a polyphase primary winding, said primary winding being provided with both a commutator cylinder and slip rings and being connected between said alternating-current systems, whereby one of said systems derives energy from the other, and means comprising revoluble commutator brushes for independently controlling the frequency of said energy.

2. The combination with two alternatingcurrent systems, only one of which has substantially balanced polyphase power, of a constant-speed dynamo-electric machine having a poly-axially closed-circuit secondary winding and a primary winding,

said primary winding being provided with both a commutator cylinder and sli rings and being connected between said a ternatquency changer, comprising a dynamo electric machine having pol phase primary windings, a commutator cyhnder connected to said (primary windings, sli rings also connecte to sald primary win ings for deriving both single-phase currents and polyphase currents, a secondary member includ mg a good damper winding, and a rotatable brush system co-operating with said commutator c linder.

In testimony whereof, I have hereunto subscribed my name this first day of Feb ruary 1921.

CHARLES LE G. FORTESCU'E. 

